Thousands of pro-democracy protesters gather to march in the streets to demand universal suffrage in Hong Kong on July 1, 2014.

HONG KONG - Tens of thousands gathered in sweltering heat in Hong Kong on Sunday to protest against a pro-democracy campaign that has threatened to shut down the city's financial district, exposing a deepening rift over political reforms in the former British colony.

The rise in tit-for-tat street protests between pro-Beijing and pro-democracy groups underscores the challenges China faces in shaping its vision for the political future of Hong Kong.

Backed largely by Beijing-friendly groups, the Alliance for Peace and Democracy says it "desires peace and no violence" and has denounced the pro-democracy Occupy Central movement that has said it will lock down the centre of the city if Beijing does not allow truly democratic elections for a leader in 2017. "We want to show that the march doesn't have to be violent and angry. It can be happy," said Robert Chow, a former Hong Kong radio host and spokesman for the alliance.

Estimates of participants in recent protests vary widely, with police saying Sunday's march drew 111,800 protesters, exceeding an estimate of more than 98,000 for a pro-democracy march on July 1.

The alliance had an initial estimate of 193,000 for Sunday's march, while organisers of the July 1 rally estimated more than 500,000 took part, as both sides jockey to reflect popular support.

The University of Hong Kong put the number on Sunday at between 79,000 and 88,000, about half the number it estimated for the July 1 protest.

The all-day event that included an early morning run and afternoon rally, which marked the end of a month-long signature campaign by the alliance, was overshadowed by speculation that some business groups had pressured people to take part.

In a centre-fold advertisement in Hong Kong's Ming Pao newspaper on Monday, the Federation of Hong Kong Shenzhen Associations said it had rallied more than 20,000 to take part in the protest, which involved nearly 1,200 other groups.

One Chinese participant surnamed Chen, who is in her 60s, said some people attended simply because they like running. "I bumped into a friend. She's running with colleagues from a property management firm. She said her firm encouraged her to run and she took part because she likes running," she added.

More people, mostly groups of elderly, showed up later in the morning to offer a flower "for peace", with different groups wearing the same coloured T-shirts and hats.

After annual protests marking the anniversary of Hong Kong's handover to China last month, hundreds of police started removing protesters from the heart of Hong Kong's business district as they tried to stage a sit-in after a rally to demand greater democracy.

Elderly Rally

"We do not support Occupy Central because it will bring trouble and instability to the city," said retiree Law Kwai-wing, 77, who said he had travelled across the border from China's Guangdong province as part of a bus tour organised by the pro-Beijing Federation of Trade Unions (FTU).

The group planned to stay for less than an hour before returning across the border from Hong Kong for lunch, which tour members would pay for themselves, he added.

Many rally participants, mostly elderly, told Reuters they were provided free transport by various political and business groups. In one district, about 150 people boarded buses organised by the Hong Kong Livestock Industry Association.

One man told Reuters said he had boarded a bus from an outlying area of Hong Kong and was given a HK$30 subsidy for lunch. "It is normal to have a little bit of a subsidy when you are at a march. Some (marches) give more, some less, but this time we only get a little money for food," said Chan Chiu-fat, 55, who was wearing a straw hat.

In a Whatsapp message seen by Reuters, people were offered HK$350 ($45) to attend the rally "for five hours". The message sender, however, declined to provide their name or background.